In drosophila melanogaster, the steroid hormone ecdysone induces a number of drastic developmental changes, the result of which is metamorphosis. In the salivary glands, the first event detected after ecdysone stimulation is the induction of transcription of specific genes, manifested as polytene chromosome puffs. At later times after ecdysone stimulation, puffs are induced at additional sites, in a developmental sequence of gene activation. It is believed that the induction of the "early puffs" is mediated by an ecdysone-binding protein, or ecdysone receptor, and that the induction of the "late puffs" is a direct consequence of the gene product of an early puff. We propose to analyze these gene induction events at the molecular level, using as an assay the formation of puffs in isolated salivary gland nuclei. We hope to identify and characterize the components involved in the developmental control of the ecdysone puffs. As a biochemical correlate to the rapid cytological assay, it will be possible to perform in situ hybridization with the RNA products of the in vitro transcription. In addition, we will concurrently analyze the so-called heat shock system of inducible genes, which is phenotypically simpler and technically easier to analyze. Thus we may also gain additional insights into the relationship of developmental and metabolic gene control.